1. Field of the Invention
The present invention relates to the use of particle monitors in a manufacturing process; and, in particular relates to the relocation of a particle filter in a loadlock chamber to accommodate particle level monitoring by a particle sensor.
2. Discussion of the Related Art
In most vacuum process equipment for semiconductor manufacturing, a loadlock is used to introduce silicon wafers from outside the equipment to the process chamber. A typical configuration is shown in FIG. 1. As shown in FIG. 1, the semiconductor wafers to be processed are brought to the process equipment 100 in a cassette 101. The loadlock chamber 102 is then vented to atmospheric pressure, and one or more wafers brought into loadlock chamber 102. Loadlock chamber 102 is then pumped down to a vacuum pressure used in the manufacturing process, and the wafers in loadlock chamber 102 are then transferred to process chamber 103.
One significant problem with the configuration of FIG. 1 is that, during the pumping process to reduce the pressure of the loadlock chamber, particles are stirred up. Many of these particles land on the wafers in loadlock chamber 102, leading to wafer contamination, while other particles are drawn into pump line 105. Since the number of particles landing on the wafer and the number of particles flowing out the pump line are both proportional to the number of particles stirred up, a direct relationship exists between the severity of wafer contamination and the count of particles in the pump line. Thus, a particle monitor measuring the particle level in the exhaust line 105 carrying gas out of the loadlock chamber 102 can provide an indication of wafer contamination in loadlock chamber 102.
In many systems, however, measurement of the particle level in the pump line 105 cannot be easily performed. This is because a particle filter 106 is installed in pump line 105 at the opening of pump line 105 into loadlock chamber 102. Particle filter 106 prevents particles such as silicon chips from being drawn onto the sealing surface of a vacuum valve located downstream in pump line 105.